Wavetek 3SR Operation Manual page 106

To begin, select a value for DC-B. This allows the video carriers to
'hit' the 3ST somewhere in the +10 dBmV range. Additional attenua-
tion can be achieved by using an in-line pad on the high side of the
diplex filter. DC-A is the directional coupler used for inserting the
forward telemetry signal and the sweep insertion points into the
system from the 3ST. By selecting the proper value for DC-A and
adjusting the forward telemetry level and forward sweep insertion
point levels in the' Sweep Transmitter' portion of the 3ST's Setup
menu, one can achieve the correct relationship between the 3ST
output signals (telemetry and sweep points) and the video carriers of
the system.
When sweeping reverse using only the 3ST in the headend, the level
of the telemetry (the telemetry coming back from the 3SRV) needs
to 'hit' the input of the 3ST at 0 dBmV ±10 dB. This can be easily
verified by checking the telemetry level in the lower right corner of
the lower right corner of the 3SRV display. Again, if additional
attenuation is required, an in-line pad on the low side of the diplex
filter may be used. If multiple nodes are being combined, a pre-
amplifier may be required. The reverse telemetry signal needs to
have a C/N > 20 dB (4.2 measurement bandwidth), which effectively
limits the number of return nodes that can be combined on the input
of the 3ST. The diplex filter is used instead of a splitter because of
better isolation and impedance matching.
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